Line-switching telecommunications networks generally connect two subscriber terminals directly to one another via a number of line sections and switching centers in order to interchange messages (for example speech, data, text and/or pictures) That is, transmission in fixed allocated timeslots. Control information and signaling messages transmitted between switching centers for connection control. When using service features. Digital, computer-controlled telecommunications networks, in particular, offer a considerably greater performance scope than analog telecommunications networks, for which reason a new powerful signaling system has been introduced in digital computer-controlled telecommunications networks.
The ITU (International Telecommunication Union) has thus specified the central signaling system no. 7 (CCS7, common channel signaling system no. 7) for line-switching telecommunications networks, and this is optimized for use in digital networks.
In contrast to the previously normal channel-based signaling, in the case of CCS7, the signaling messages are passed via separate signaling paths or signaling data channels. One signaling data channel in this case transports the signaling messages for a large number of user channels.
In a line-switching telecommunications network, the signaling data channels for CCS7 connect so-called message transfer points (MTP) to one another. These message transfer points together with the signaling channels thus form an autonomous signaling network, which is superimposed on an associated user channel network.
Signaling points (SPC, signaling point code) are in this case the sources and sinks of the signaling traffic within the line-switching telecommunications network, and are primarily formed by switching centers or signaling nodes. In this case, the message transfer points transmit received signaling messages preferably using a destination address (destination point code, DPC) to another message transfer point. Such a message transfer point may either be integrated in a signaling end point, i.e. a switching center, or may form a dedicated signaling node in the signaling network. Furthermore, depending on the size of the signaling network, one or more levels of such message transfer points are possible.
All signaling points (SPC, signaling point code) in a predetermined signaling network are identified by, for example, a 14-point code within a numbering plan defined by the ITU, and can thus be addressed specifically in a signaling message. In the central signaling system no. 7 (CCS7), such a signaling message is provided by the message signaling unit (MSU, message signal unit).
In addition to the destination address (destination point code, DPC) and a source address (origin point code, OPC), a speech circuit address (circuit identification code, CIC) is essentially also stored in these signaling messages or message signaling units (MSU) transmitted in the signaling network. This speech circuit address (CIC) has 12 bits according to the ITU Standard, which are used to allocate the signaling message to a specific user channel. A speech circuit address (CIC) is in this case permanently allocated to each user channel, thus resulting in an extremely efficient line-switching telecommunications network.
However, as a result of the tremendous development of the INTERNET, there is an increasing need to connect such conventional line-switching telecommunications networks to so-called packet-switching or packet-oriented telecommunications networks, such as the INTERNET. However, as has already been mentioned above, since a line-switching telecommunications network with an associated signaling network represents an essentially closed system, a large number of problems arise if two telecommunications networks are simply coupled together.
FIG. 1 shows a simplified illustration of such different telecommunications networks, which are connected to one another via a conventional gateway. According to FIG. 1, the line-switching telecommunications network 1 (PSTN, public switched telecommunication network) comprises a large number of switching centers 3 and 4 (VST), which are connected via a large number of user and signaling channel data interfaces (lines). By way of example, a subscriber terminal device 6 (TE) is connected to at least one of the switching centers of the line-switching telecommunications network 1.
A gateway 5, which converts both the user channel data and the signaling channel data to the appropriate formats for the respective telecommunications networks is therefore required to produce a connection for a further subscriber terminal 7 (TE) which is connected to a packet-switching or packet-oriented telecommunications network 2 (INTERNET). To be more precise, and as shown in FIG. 1, the switching center 3 is connected via a user channel data interface and a signaling channel data interface to the gateway 5. On the other hand, the gateway 5 represents a data interface IP to the packet-switching telecommunications network 2, which is preferably the INTERNET. This results in the two different telecommunications networks being connected in a relatively simple manner, and this is normally referred to as a “stand-alone gateway”.
However, conventional solution is subject to a disadvantage due to the fact that the gateway 5 must receive an additional signaling point code SPC3 in order that it can be specifically selected or addressed via the central signaling system no. 7 of the line-switching telecommunications network 1. In consequence, this means that, when there are a large number of such “stand-alone gateways”, there must be a massive enlargement in terms of the signaling point codes SPC for the telecommunications network 1, which on the one hand is extremely costly and on the other hand involves a high risk for the intrinsically closed network structure, since each new element changes the network structure and can cause unpredictable disturbances in the telecommunications network.
FIG. 2 shows a further option for providing a gateway for connecting different telecommunications networks, based on an unpublished company-internal prior art. The same reference symbols in this case denote the same or similar elements, for which reason they will not be described in detail in the following text.
In order to avoid enlarging the signaling point code by introducing a stand-alone gateway, the gateway as shown in FIG. 2 is subdivided into a user channel data converter 50′ and a signaling channel data converter 51′, with the user channel data converter 50′ converting only that user channel data which comes from the switching center 3 to a corresponding IP format. The actual evaluation and conversion of the signaling data is carried out in the switching center 3 or in a signaling channel data converter 51′ which is directly integrated in it and which actuates the user data channel converter 50′ via a specific signaling data interface MGCP (media gateway control protocol) in order to select appropriate address information for the packet-switching telecommunications network 2. Consequently, the extremely critical enlargement of the signaling point code (SPC) in the line-switching telecommunications network is avoided, since the switching center 3, with its signaling point code SPC1, now provides not only the gateway and the user channel data converter 50′ but also the message transfer point for the switching center 3 in the central signaling system no. 7 for the line-switching telecommunications network 1. Since the network structure is not changed, there is no risk of disturbances in the telecommunications network 1, which continues to have extremely short downtimes. However, a solution such as this has the disadvantage that a manufacturer of such a solution must have very detailed knowledge of the respective switching centers in the line-switching telecommunications network 1 and, in consequence, this can be done only by system manufacturers of the telecommunications network 1.
A further option (not illustrated) for providing a gateway for connecting different telecommunications networks is to provide the user channel data converter 50′, which is illustrated in FIG. 2, such that it is likewise integrated in the switching center 3, so that there are no external components whatsoever, and a solution can be offered, “from the same source”. However, like the solution described above, this is likewise disadvantageous owing to the fact that only system manufacturers with detailed knowledge of the respective switching center 3 can provide such integration of the gateway.
Furthermore, the document Anquetil L-P et al.: “Media Gateway Control Protocol and Voice over IP Gateways”, Electrical Communication, Alcatel Brussels, BE, 1 Apr. 1999, pages 151–157 uses a media gateway controller for connecting a line-switching telecommunications system based on SS7 to a packet-switching telecommunications system based on the IP. Complex signaling gateways are in this case used for passing on the signaling information.